The invention relates to the field of circuit breakers and more particularly to a drive mechanism for a circuit breaker with a spring which is tensionable by means of a crank top seated on a shaft through a rotatingly drivable eccentric member, a transmission member and a directional lock seated on the shaft.
Drive mechanisms of this type are used in many different designs in order to tension a relatively strong spring, with sufficient energy potential to turn the circuit breaker on and off again either manually or with the aid of a small motor. Thus the drive mechanism can function as a step drive, in which after the motor is turned on, the spring is tensioned far enough to store the required energy for the subsequent release of the switch mechanism. Alternatively the drive mechanism can operate as a storage drive, in which the energy stored by the spring can be released in any desired manner at a desired moment for switching. Such drive mechanisms are produced generally in very similar designs for both low- and medium-voltage circuit breakers. An example of such a drive mechansim can be seen in a low-voltage circuit breaker disclosed in U.S. Pat. No. 3,301,984. In that circuit breaker, the transmission member is a rod driven by an eccentric crank pin which acts on the supports of a drive catch movable around the shaft, locking into the cogs of a ratchet wheel and further rotating said wheel stepwise as a result of the to-and-fro movement of the rod.
A locking catch working similarly on the cogs thereby prevents reverse rotation of the ratchet wheel under the influence of the spring to be tensioned. Because of the high reliability requirements and durability of drive mechanisms of the type considered here, considerable expense on the accuracy of the mutually activated parts and on their resistance to deformation and wear cannot to be avoided. In particular, careful alignment of the transmission member stroke to the ratchet wheel divisions is required. If the transmission member stroke is too small, the ratchet wheel is not rotated further, while an uneconomic idle stroke occurs if the transmission member stroke is too large in relation to the ratchet wheel divisions. Moreover, in this case the ratchet wheel cogs, drive catch and its bearing will be subjected to excessive strain. A further problem is created by the transmission member, which on the one hand can hinder desired positioning of certain circuit breaker components within the rather sophisticated overall assembly, and on the other hand is the source of unavoidable length tolerance problems.
In mechanical engineering it is well known that by utilizing flexible traction and directional lock, a to-and-fro motion can be converted to a stepwise unidirectional rotary motion, see French Patent No. A-756,886. For traction, chains are used guided via chain wheels which incorporate a clamp-roll freewheel serving as directional lock. The chains are held tight by a spring and the chain wheels actuated by restoring force.
It is an object of the invention to eliminate the length tolerance problem, and the massiveness and cumbersomeness characteristics of reliable and durable equipment found in drive mechanisms of the initially named type by use of said flexible traction.